1. Field of the Invention
The present invention relates to a movable contact unit used in operation units of various electronic apparatuses, a method of manufacturing the movable contact unit, and a method of manufacturing a switch panel.
2. Background Art
Recently, various electronic apparatuses such as portable phones or personal digital assistants (PDAs) have been remarkably downsized and have had many functions. As an operation unit of each of the electronic apparatuses, a switch panel formed by disposing a plurality of pressing switches arranged in a predetermined array is used.
A conventional movable contact unit used for forming such a switch panel and an electronic apparatus mounted with the switch panel using the movable contact unit are described with reference to FIG. 4 to FIG. 6.
FIG. 4 is a sectional view of the conventional movable contact unit, and FIG. 5 is an exploded perspective view thereof. Movable contact 1 made of an elastic thin metal sheet has a dome shape having a downward opening. Base sheet 2 is made of an insulating resin film, and has adhesive layer 2A on its lower surface. A plurality of movable contacts 1 are disposed in a predetermined array on the lower surface of base sheet 2, and the upper surface of each movable contact 1 is stuck and held by adhesive layer 2A. Thus, movable contact unit 3 capable of forming a plurality of pressing switches is formed.
FIG. 6 is a sectional view of an essential part of an electronic apparatus mounted with the switch panel formed using the conventional movable contact unit. A plurality of pairs, each of which includes central fixed contact 5A and outer fixed contact 5B that correspond to respective movable contact 1, are disposed on the upper surface of planar wiring board 4 at positions corresponding to respective movable contacts 1. An electrode for connection to another circuit is led from each fixed contact, although they are not illustrated.
The lower end of the outer periphery of each movable contact 1 is mounted on each corresponding outer fixed contact 5B. The lower surface of the top of the dome shape faces each corresponding central fixed contact 5A. Movable contact unit 3 is overlaid on wiring board 4 with reference to small holes 4A for positioning that are disposed at ends and small holes 2B of base sheet 2. Movable contact unit 3 is stuck onto wiring board 4 through exposed adhesive layer 2A of base sheet 2. Thus, switch panel 7 having a plurality of arranged press switches is formed.
Switch panel 7 is positioned in exterior case 8 of an electronic apparatus. Each operation button 9 is disposed at a position corresponding to each movable contact 1 of switch panel 7. Operation button 9 vertically movably projects from a button hole in exterior case 8 and is an operation portion that can be pressed from the outside.
An operation of such an operation unit of the electronic apparatus is described briefly. Firstly, operation button 9 is pressed down to press the upper surface of the top of movable contact 1 with operation button 9. Then, movable contact 1 is elastically inverted while providing a click feeling. When the lower surface of the top makes contact with central fixed contact 5A, central fixed contact 5A is electrically connected to outer fixed contact 5B via movable contact 1. The press switch is thus turned on.
When the pressing force to operation button 9 is released, the lower surface of the top is separated from central fixed contact 5A by the elastic restoring force of movable contact 1, and operation button 9 is pressed back. The press switch is thus returned to the OFF state shown in FIG. 6. Such a panel switch is disclosed in Japanese Patent Unexamined Publication No. 2003-077368, for example.
As the material of movable contact 1, a thin stainless-steel sheet is often used. However, such a material can be magnetized due to its handling or the like. This magnetization can affect the operation of a magnetic sensor that is mounted on a portable phone or the like and used for determination of a folded (closed) state or unfolded (open) state of the portable phone or azimuth identification. Therefore, when the integration density of components is increased in an apparatus, consideration of the effect of the magnetization of movable contact 1 is required.